The present invention relates to tape recorders, and, more particularly, to a tape path assembly for a streaming tape drive.
Streaming tape drives are high-speed bulk data transfer devices. They have been finding increasing application, for example, as cost-effective archiving and back-up devices for hard disk storage.
In order to handle high-speed bulk data transfers, streaming tape drives can be designed to read and write synchronous parallel tracks of information on rapidly moving magnetic tape media in a relatively dense format.
The basic components of a streaming tape drive include a supply reel, a take-up reel, drive motors for each of the reels, and a head assembly providing read/write and erase functions. Other typical components are tape guides on either side of the head assembly to precisely position the tape on the heads, and a buffer means to maintain tape tension and minimize slack in the tape. In addition, a position sensor, associated with the buffer means, and a tape speed sensor are provided to servo the drive motors and otherwise provide operational feedback to the streaming tape drive system.
One major challenge of high-performance streaming tape drives is that the precise reading and writing of dense parallel tracks imposes severe constraints on the mechanical tolerances of the drive. Misalignment of the tape relative to a read/write head can skew the parallel tracks of data, impairing or at least complicating the operation of a read circuit. Similar problems occur due to elastic and inelastic deformation of the tape itself due to the stresses involved in moving, starting and stopping the tape during operation of the drive.
Some of the more subtle errors due to misalignment can be corrected, for example, by de-skew circuitry. However, there are limits to what can be reliably corrected. De-skew and error correction circuits are not completely effective even at correcting minor errors, and more severe errors, e.g., a tape track being read into the wrong data path at the read head, might preclude correction entirely.
Furthermore, since detected but uncorrected errors are often dealt with by backing up the drive and rereading a portion of the tape, errors due to misalignment propagate themselves. In other words, uncorrected errors result in more stopping and starting of the drive, resulting in more stress on the tape, resulting in greater tape deformation, resulting in greater track-to-track misalignment.
Typically, most of the tape path components affecting tape alignment are mounted on a main casting for the tape recorder. Thus, the tape buffer, a first tape guide, the tape head assembly, a second tape guide and a speed sensor must be precisely positioned with respect to the common casting so that their alignments are properly coordinated. Misalignments can be induced by individual subassembly misalignments, or by deformation of the main casting due to mechanical or thermal stresses. In addition, deformation can cause misalignment over the section of tape extending along the tape path between the supply and take-up reels.
Another problem with the current arrangement is the difficulty of repair. A service person replacing a component is required to replace a single tape path component with the precision required by the mechanical tolerance specifications of the recorder. In addition to the mechanical adjustments, the sensors can require sensitive electronic adjustments upon replacement. For example, a service person might be required to adjust internal potentiometers to set the zero and gain of a tape buffer position sensor.
Since a manufacturer tends to have less control over service personnel than it does its manufacturing personnel, there are greater opportunities for variations in skill. Furthermore, service people are often required to service a great variety of products, and it is difficult for them to be versed in the details of and carry the tools for all service problems for all serviced goods.
Another problem with position sensors arises when they are used to determine when a buffer arm is out of range. For example, an "out of range" signal can be created by comparing the buffer arm position sensor voltage output with a fixed voltage. This approach requires a very accurate and low draft position voltage output from the buffer arm subassembly, and usually requires adjustments. As a result, manufacturing costs are increased, and problems with servicing are exacerbated.
An alternative approach has been to create an "out of range" signal by an optical switch and shutter mounted on the shaft of the buffer arm. This requires extra parts, and can also require adjustments.
What is needed is a streaming tape drive design which provides conveniently for tight mechanical tolerances while also simplifying demands on service personnel. Mechanical tolerances should be improved by reducing the causes of tape distortion, which can also induce misalignment, as well as by providing better mutual alignment of tape path components.